There are many applications where ultraviolet (UV) light sources are used for treating liquids. The applicant of the present application, Wallenius Water AB in Sweden, has developed and is selling water treatment equipment having a water purifier comprising an elongated tubular treatment chamber with an inlet and an outlet. In the center of the treatment chamber a generally tubular quartz glass is arranged and inside the quartz glass a UV source, such as a lamp capable of generating wavelengths in the UV region. Low pressure UV lamps offer great efficiency and find particular application e.g. in the disinfection of water. Examples of different types of low pressure lamps include e.g. ozone-free mercury low pressure lamps, mercury ozone-generating low pressure lamps, and U-shaped lamps which supply high power in a compact design.
The inner surface of the treatment chamber of the water treatment equipment may be covered with catalytic material, such as titanium dioxide, which catalysts promotes and increases the amount of treatment material. The treatment equipment also comprises a pumping device which pumps liquid from e.g. a tank into the treatment chambers.
The liquid that is treated often comprises particles and other solid matter other than the organisms that are killed off by the treatment units. These particles, as well as other residue from the killed off organisms, have a tendency to stick on the interior surfaces of treatment units. These particles, and other residue, aggregated on the surface are generally denoted as fouling.
UV light treatment, more specifically UV-light in combination with heat, sometimes provokes chemical reactions resulting in depositions on the interior surfaces, e.g. at the outer surface of the quarts sleeve. These resulting depositions are generally denoted as scaling. Often scaling is more difficult to remove from the surface than fouling. Furthermore, uneven and lumped deposits of fouling and/or scaling on the interior surfaces of the devices that are even more difficult to remove are a commonly occurring problem.
This means that in order to have an optimum efficiency of the treatment device the interior has to be cleaned regularly. According to one solution in the prior art, cleaning is performed by injecting cleaning liquids into the treatment chamber, where the cleaning liquids are developed for removing the fouling or scaling on the surfaces. However, even if they are efficient for removing fouling/scaling and the like deposits on the surfaces of the treatment chambers, they require that the treatment units are closed down during a period of time, whereby thus no treatment of liquid may be performed.
Similar arrangements are also described by others within the field as exemplified by the following.
U.S. Pat. No. 7,425,272 relates to a system for cleaning protective sleeves in UV decontamination systems. The disclosed system for cleaning the outer surface of a quartz sleeve is based on the recognition that providing a honing material (e.g. a photocatalytic slurry comprising TiO2) with a predetermined abrasiveness through the annulus at high velocity works to remove aggregated particles from the outer surface. In U.S. Pat. No. 7,425,272 the linear velocity of a slurry material passing through the annulus during a cleaning process is about 1 m/s, and in one particular example it is stated that the velocity is at least 0.5 m/s.
Also U.S. Pat. No. 5,124,131 and U.S. Pat. No. 5,626,768 relate to UV-radiation treatment systems and methods where a liquid is moved along a UV-radiation source.
U.S. Pat. No. 5,625,194 relates to an apparatus for continuous cleaning of tubular lamp wells for UV-light producing lamps. A large number of small plastic pellets are dispersed in the reaction solution and maintained in turbulent motion by a stirrer in the reactor. The pellets frequently impact the outer surface of the tubular wells with sufficient momentum to prevent deposits of material from adhering on the tubular wells.
Hence, there is still a need in the art for an improved liquid treatment module which is less prone to suffer from problems associated with scaling and/or fouling building up on the interiors of the module during liquid treatment.
In addition there is a demand for an improved functionality of the treatment module to ensure that as much liquid as possible is treated, i.e. exposed, to a predefined lowest UV-light treatment dose.